Research On High Performance Three-dimensional Graphene/CNT Nanocomposite Sodium Metal Anode And Full Battery

With the increasing demand for electronic products in human life,lithium ion battery（LIB）has become the main power supply for electronic products.Similar to the working principle of LIB,sodium ion battery（SIB）has comparable energy and power densities.However,sodium,which is abundant and cheap on earth,is expected to dominate the next generation of energy-storage systems.Among various anode materials of SIB,metallic sodium anode is considered as the most potential anode material due to its high theoretical capacity(1166 mA h g^-1)and the lowest electrochemical potential（-2.714 V vs.standard hydrogen electrode）.However,the sodium metal anode faces great challenges:uneven deposition,infinite volume expansion,dendrite problems,and unstable solid-electrolyte-interface（SEI）membranes during sodium plating/stripping severely limit the development of sodium metal anode.In order to solve the dendrite problem and according to the Sand’s time formula of electrodeposition dendrite growth,this paper proposes to use three-dimensional graphene foam/carbon nanotubes（3D GF/CNT）as the host of sodium metal to inhibit sodium dendrite and improve the electrochemical performance of sodium metal anode electrode.In addition,this paper prepared the composite of Na₃V₂（PO₄）₂O₂F（NVPOF）and reduced graphene oxide（rGO）（represented as NVPOF@rGO）as a cathode electrode,which matched with the anode electrode of Na@GF/CNT for sodium ion full battery.The specific research contents and results are as follows:（1）3D GF/CNT three-dimensional structure with a large specific surface area and reducing current density was constructed,thereby inducing uniform deposition of sodium ions,which effectively inhibits the formation of dendrites and stabilizes the SEI film.At the same time,the excellent flexibility and abundant porous space structure in 3D GF/CNT can adapt to the large volume change of sodium metal during the repeated plating/stripping process.3D GF/CNT was used as the stable host of sodium metal to study the electrochemical behavior of sodium metal depositing on it,including the evolution of deposition morphology and electrochemical performance testing.Electrochemical tests show that at a high current density of 4 mA cm^-2,the overpotential is only 15 mV,which can steadily cycle for more than 450 cycles.（2）Graphene oxide（GO）was coated on the surface of NVPOF by the method of positive and negative charge mutual attraction.NVPOF@rGO composite was prepared by annealing treatment and used as the cathode material of SIB.The focus is on the storage behavior and performance of Na ions in NVPOF@rGO composites,especially the migration rate of Na ions in NVPOF@rGO materials.Experimental data shows that rGO can significantly improve the conductivity and increase the migration rate of Na ions.Among them,the NVPOF@rGO-5 nanocomposite exhibits the most excellent cycle performance and rate performance.At a high rate of 5 C,it can still maintain a capacity of 61.2 mA h g^-1 after 1000 cycles,and the capacity retention rate is 85%.The average Coulombic efficiency is as high as 99.5%.（3）Na@GF/CNT was used as the anode electrode,and NVPOF@rGO composite material was used as the cathode electrode to prepare a full battery,and its electrochemical performance was initially tested.The results showed that the initial discharge capacity of the full battery with Na@GF/CNT as the anode electrode was 100 mA h g^-1.